In on-going studies of humoral and cell-mediated immune responses immunoregulatory determinants playing a role in the immunopathogenesis of EAE, the following lines of investigation will be pursued: (a) nature of the moiety or moieties produced by sensitized donor Lewis rats responsible for transfer of EAE to normal syngeneic recipients, (b) factors modulating susceptibility and refractoriness, to EAE in adult and new born Lewis rats, respectively, and (c) mode of EAE-adjuvant action, including role of IgE induction by pertussis vaccine.